Query folders and multiple files

In this article, you'll learn how to write a query using SQL on-demand (preview) in Azure Synapse Analytics.

SQL on-demand supports reading multiple files/folders by using wildcards, which are similar to the wildcards used in Windows OS. However, greater flexibility is present since multiple wildcards are allowed.

Prerequisites

Your first step is to create a database where you'll execute the queries. Then initialize the objects by executing setup script on that database. This setup script will create the data sources, database scoped credentials, and external file formats that are used in these samples.

You'll use the folder csv/taxi to follow the sample queries. It contains NYC Taxi - Yellow Taxi Trip Records data from July 2016 to June 2018. Files in csv/taxi are named after year and month using the following pattern: yellow_tripdata_-.csv

Read all files in folder

The example below reads all NYC Yellow Taxi data files from the csv/taxi folder and returns the total number of passengers and rides per year. It also shows usage of aggregate functions.

SELECT 
    YEAR(pickup_datetime) as [year],
    SUM(passenger_count) AS passengers_total,
    COUNT(*) AS [rides_total]
FROM OPENROWSET(
        BULK 'csv/taxi/*.csv',
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0',
        FIRSTROW = 2
    )
    WITH (
        pickup_datetime DATETIME2 2, 
        passenger_count INT 4
    ) AS nyc
GROUP BY
    YEAR(pickup_datetime)
ORDER BY
    YEAR(pickup_datetime);

Note

All files accessed with the single OPENROWSET must have the same structure (i.e., number of columns and their data types).

Read subset of files in folder

The example below reads the 2017 NYC Yellow Taxi data files from the csv/taxi folder using a wildcard and returns the total fare amount per payment type.

SELECT 
    payment_type,  
    SUM(fare_amount) AS fare_total
FROM OPENROWSET(
        BULK 'csv/taxi/yellow_tripdata_2017-*.csv',
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0',
        FIRSTROW = 2
    )
    WITH (
        payment_type INT 10,
        fare_amount FLOAT 11
    ) AS nyc
GROUP BY payment_type
ORDER BY payment_type;

Note

All files accessed with the single OPENROWSET must have the same structure (i.e., number of columns and their data types).

Read folders

The path that you provide to OPENROWSET can also be a path to a folder. The following sections include these query types.

Read all files from specific folder

You can read all the files in a folder using the file level wildcard as shown in Read all files in folder. But, there's a way to query a folder and consume all files within that folder.

If the path provided in OPENROWSET points to a folder, all files in that folder will be used as a source for your query. The following query will read all files in the csv/taxi folder.

Note

Note the existence of the / at the end of the path in the query below. It denotes a folder. If the / is omitted, the query will target a file named taxi instead.

SELECT
    YEAR(pickup_datetime) as [year],
    SUM(passenger_count) AS passengers_total,
    COUNT(*) AS [rides_total]
FROM OPENROWSET(
        BULK 'csv/taxi/',
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0',
        FIRSTROW = 2
    )
    WITH (
        vendor_id VARCHAR(100) COLLATE Latin1_General_BIN2, 
        pickup_datetime DATETIME2, 
        dropoff_datetime DATETIME2,
        passenger_count INT,
        trip_distance FLOAT,
        rate_code INT,
        store_and_fwd_flag VARCHAR(100) COLLATE Latin1_General_BIN2,
        pickup_location_id INT,
        dropoff_location_id INT,
        payment_type INT,
        fare_amount FLOAT,
        extra FLOAT,
        mta_tax FLOAT,
        tip_amount FLOAT,
        tolls_amount FLOAT,
        improvement_surcharge FLOAT,
        total_amount FLOAT
    ) AS nyc
GROUP BY
    YEAR(pickup_datetime)
ORDER BY
    YEAR(pickup_datetime);

Note

All files accessed with the single OPENROWSET must have the same structure (i.e., number of columns and their data types).

Read all files from multiple folders

It's possible to read files from multiple folders by using a wildcard. The following query will read all files from all folders located in the csv folder that have names starting with t and ending with i.

Note

Note the existence of the / at the end of the path in the query below. It denotes a folder. If the / is omitted, the query will target files named t*i instead.

SELECT
    YEAR(pickup_datetime) as [year],
    SUM(passenger_count) AS passengers_total,
    COUNT(*) AS [rides_total]
FROM OPENROWSET(
        BULK 'csv/t*i/', 
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0',
        FIRSTROW = 2
    )
    WITH (
        vendor_id VARCHAR(100) COLLATE Latin1_General_BIN2, 
        pickup_datetime DATETIME2, 
        dropoff_datetime DATETIME2,
        passenger_count INT,
        trip_distance FLOAT,
        rate_code INT,
        store_and_fwd_flag VARCHAR(100) COLLATE Latin1_General_BIN2,
        pickup_location_id INT,
        dropoff_location_id INT,
        payment_type INT,
        fare_amount FLOAT,
        extra FLOAT,
        mta_tax FLOAT,
        tip_amount FLOAT,
        tolls_amount FLOAT,
        improvement_surcharge FLOAT,
        total_amount FLOAT
    ) AS nyc
GROUP BY
    YEAR(pickup_datetime)
ORDER BY
    YEAR(pickup_datetime);

Note

All files accessed with the single OPENROWSET must have the same structure (i.e., number of columns and their data types).

Since you have only one folder that matches the criteria, the query result is the same as Read all files in folder.

Multiple wildcards

You can use multiple wildcards on different path levels. For example, you can enrich previous query to read files with 2017 data only, from all folders which names start with t and end with i.

Note

Note the existence of the / at the end of the path in the query below. It denotes a folder. If the / is omitted, the query will target files named t*i instead. There is a maximum limit of 10 wildcards per query.

SELECT
    YEAR(pickup_datetime) as [year],
    SUM(passenger_count) AS passengers_total,
    COUNT(*) AS [rides_total]
FROM OPENROWSET(
        BULK 'csv/t*i/yellow_tripdata_2017-*.csv',
        DATA_SOURCE = 'sqlondemanddemo',
        FORMAT = 'CSV', PARSER_VERSION = '2.0',
        FIRSTROW = 2
    )
    WITH (
        vendor_id VARCHAR(100) COLLATE Latin1_General_BIN2, 
        pickup_datetime DATETIME2, 
        dropoff_datetime DATETIME2,
        passenger_count INT,
        trip_distance FLOAT,
        rate_code INT,
        store_and_fwd_flag VARCHAR(100) COLLATE Latin1_General_BIN2,
        pickup_location_id INT,
        dropoff_location_id INT,
        payment_type INT,
        fare_amount FLOAT,
        extra FLOAT,
        mta_tax FLOAT,
        tip_amount FLOAT,
        tolls_amount FLOAT,
        improvement_surcharge FLOAT,
        total_amount FLOAT
    ) AS nyc
GROUP BY
    YEAR(pickup_datetime)
ORDER BY
    YEAR(pickup_datetime);

Note

All files accessed with the single OPENROWSET must have the same structure (i.e., number of columns and their data types).

Since you have only one folder that matches the criteria, the query result is the same as Read subset of files in folder and Read all files from specific folder. More complex wildcard usage scenarios are covered in Query Parquet files.

Next steps

More information can be found in the Query specific files article.